This document specifies a standard interface between web servers and
Perl web applications or frameworks, to promote web application
portability and reduce the duplicated efforts by web application
framework developers.

Keep in mind that PSGI is not Yet Another web application framework.
PSGI is a specification to decouple web server environments from web
application framework code. PSGI is also not the web application API.
Web application developers (end users) are not supposed to run their web
applications directly using the PSGI interface, but instead are
encouraged to use frameworks that support PSGI, or use the helper
implementations like Plack (more on that later).
